These levels come from outside activities that penetrate the classroom structure, from teaching activities, and other noise generated inside, which can be exacerbated by room reverberation.

这些（噪音）可以是穿透教室建筑结构的室外活动声、教学活动的声音以及室内产生的其它各种声响，这些声音都会因为房间的回声效果而被放大。